Conventional lock devices of this type are applied to steering lock devices for inhibiting and allowing the rotation of a steering wheel, shift lock devices for inhibiting and allowing the movement of a select lever of an automatic transmission, and the like. For example, a conventional steering lock device includes a cam member which rotates in an unlocking direction and a locking direction while interlocking an operation of a key knob, and a cam contact surface in contact with a sliding surface of the cam member. The conventional steering lock device further includes a lock member which follows the movement of the sliding surface of the cam member so as to move between an unlocking position for allowing the rotation and movement of the steering shaft as a movable member and a locking position for inhibiting the rotation of a steering shaft (e.g., see the following patent document: Japanese Utility Model Registration Publication No. 2530045).
In such a manually-operated device, even if the rotary torque necessary for rotating the cam member is large in a partial range or has variations, an operator can easily rotate the cam member only by applying a force. Accordingly, the cam profile of the sliding surface of the cam member is designed with importance placed on rotation angles from the start of the operation to the end of the operation but no importance placed on an unlocking force.
However, in the case of an electric steering lock device, the cam profile of a sliding surface of a cam member needs to be determined, so that a load on a motor serving as a drive source does not become large. Here, it is conceivable to design the cam profile of the sliding surface of the cam member, so that the shift stroke amount of a lock member per rotation angle of the cam member can be maintained constant.